Re: devfs vs. udev

Greg KH
2003-10-07T17:53:21Z

On Tue, Oct 07, 2003 at 02:38:27PM +0200, Måns Rullgård wrote:
>
> I noticed this in the help text for devfs in 2.6.0-test6:
>
> Note that devfs has been obsoleted by udev,
> <http://www.kernel.org/pub/linux/utils/kernel/hotplug/>.
> It has been stripped down to a bare minimum and is only provided for
> legacy installations that use its naming scheme which is
> unfortunately different from the names normal Linux installations
> use.
>
> Now, this puzzles me, for a few of reasons. Firstly, not long ago,
> devfs was spoken of as the way to go, and all drivers were rewritten
> to support it. Why this sudden change?

A few things happened:
- the devfs maintainer/author disappeared and stoped maintaining
the code.
- devfs was found to have unfixable bugs
- it was determined that the same thing could be done in
userspace (like udev.)

> Secondly, that link only leads me to a package describing itself as an
> experimental proof-of-concept thing, not to be used for anything
> serious. How can something that incomplete obsolete a working system
> like devfs?

I didn't send that patch to the kernel to mark devfs as such.

Actually devfs is still very much "experimental" and "proof-of-concept"
if you have ever looked at it's code :)

> Thirdly, udev appears to respond to hotplug events only. How is it
> supposed to handle device files not corresponding to any physical
> device?

Like what? Anything that shows up in sysfs, udev will handle. It's
only a matter of getting everything to show up in sysfs now... It's
almost all there.

> Finally, I quite liked the idea of a virtual filesystem for /dev. It
> reduced the clutter quite a bit. As for the naming scheme, it could
> easily be changed.

devfs's naming scheme could easily be changed? Hahaha...

udev will be a major factor of improvement for changable naming schemes.
Please read the OLS paper for more details.

thanks,

greg k-h